Centromeric localization of KNL2 and CENP-C proteins in plants depends on their centromere-targeting domain and DNA-binding regions
In eukaryotic organisms, proper chromosome segregation during cell division depends on the centromeric histone H3 (CENH3) variant. Our previous studies identified a plant CENH3 assembly factor, Kinetochore Null2 (KNL2), that possesses a centromere-targeting motif, CENPC-k, similar to the CENPC motif in CENP-C. Additionally, we have demonstrated that KNL2 can bind DNA in vitro, independent of its CENPC-k motif. Thus, the mechanism underlying the binding of KNL2 to centromeric DNA remains elusive. Our study shows that the CENPC-k and CENPC motifs alone are not sufficient to target the centromere in N. benthamiana and A. thaliana. In-silico analysis revealed flanking DNA-binding regions near the CENPC-k and CENPC motifs, suggesting their importance in interacting with centromeric DNA. Fusion of protein fragments containing these motifs to EYFP facilitated targeting to the centromere. Deletion of DNA-binding domains reduced the centromeric localization of KNL2-C, whereas fusion of CENPC-k to the H-NS protein from E. coli targeted it to centromeres. We conclude that targeting of KNL2 and CENP-C proteins to centromeres is dependent on the CENPC-k/CENPC motifs, and their sequence-independent DNA-binding promotes anchoring at the centromere. Understanding the targeting mechanisms of KNL2 and CENP-C may help to engineer kinetochore structure by targeting chromatin modifying proteins to centromeres.